SINOPEC Sanren EVA 7.5/1.5

What Processing Limits Govern Coextruded Greenhouse Film Based on a 7.5 wt% VA Copolymer?

In blown film lines producing 150–200 µm greenhouse covers, SINOPEC Sanren EVA 7.5/1.5 is let down at 25 wt% to 35 wt% into LDPE with melt flow rate 0.3 g/10 min to 0.7 g/10 min; up to 10 wt% mLLDPE is added to maintain dart impact after UV stabiliser incorporation. The nominal melt flow rate of the grade is 1.5 g/10 min when determined per ISO 1133-1:2022 at 190 °C under 2.16 kg load, and the vinyl acetate content is 7.5 wt%. The VA segment improves stress-crack resistance in contact with metal frame wire and increases long-wave infrared retention relative to LDPE, but the 1.5 g/10 min melt flow rate limits throughput on high-shear grooved-feed extruders. Melt temperature is held between 165 °C and 195 °C; sustained operation above 205 °C triggers acetic acid elimination and gel formation, which appears as bubble instability and rising screen-pack pressure. On a 65 mm extruder with 30:1 L/D and die diameter 350 mm, die gap is set at 1.8 mm to 2.4 mm, blow-up ratio from 2.0 to 3.2. Pre-drying is not required when storage relative humidity is below 60%; otherwise hopper drying at 60 °C to 65 °C for 2 h to 4 h prevents surface streaking. UV stabiliser masterbatch is dosed at 1.5 wt% to 2.5 wt%, with HALS and benzophenone absorbers. Film gauge control requires internal bubble cooling and automatic die bolt adjustment because melt strength fluctuations below 165 °C produce gauge bands beyond ±5%. Compliance testing follows EN 13206:2017 for greenhouse cover film, with tensile properties per ISO 527-3, elongation at break measured on 15 mm wide strips at 500 mm/min, and dart impact per ISO 7765-1 Method A. The finished product is a three-layer greenhouse cover of 180 µm nominal thickness; the EVA-containing core layer provides puncture resistance during installation and seasonal wind loading, while outer LDPE layers carry UV stabilisers and antifog additive packages. The film is not recommended for contact with copper-containing pesticide sprays, because copper ions accelerate thermo-oxidative degradation of the VA segment.

Heavy-duty industrial sack extrusion on 70 mm smooth-bore extruders uses the same grade at 15 wt% to 25 wt% in blends with LLDPE and LDPE for flat films and side-gusset tubing of 100 µm to 150 µm. The low melt index raises melt strength and bubble stability when the blow-up ratio exceeds 2.5. Barrel temperatures are set at 160 °C to 190 °C; die head temperature is maintained at 180 °C to 195 °C. In coextruded sacks the EVA-rich layer is placed in the core, with outer layers of LLDPE containing 0.1 phr to 0.3 phr slip and antiblock. The final sacks are used for packaging glass fibre insulation, polymer chips, and construction aggregate; the EVA modification resists pinhole formation and tearing during filled drop tests. Compliance for dangerous goods packaging is assessed under the UN Manual of Tests and Criteria, Part III, drop and stacking tests rather than by resin-level certification alone. Fabricators report lower burst failure on side gussets at 45 kg to 50 kg fill weight when EVA replaces 5 wt% to 10 wt% of LDPE in the core, but published data for this specific grade is limited. Screw speed is normally limited to 80 rpm to 100 rpm because melt pressure above 32 MPa at the screen pack produces melt fracture and uneven film thickness. Copper-alloy thermocouple wells and die parts are avoided because residual acetic acid at processing temperature attacks copper and accelerates degradation.

Blown Film Die Pressure and Melt Fracture Thresholds

High-shrink industrial collation film uses the grade at 20 wt% to 30 wt% with mLLDPE and LDPE in a double-bubble line. The primary tube extruder is a 65 mm machine with 30:1 L/D, die gap 1.5 mm, and melt temperature 185 °C to 205 °C; the secondary orientation oven is maintained at 110 °C to 125 °C. Machine-direction stretch ratios range from 4:1 to 5:1, and transverse-direction stretch ratios from 4:1 to 6:1. The 1.5 g/10 min melt flow rate raises orientation stress but also increases resistance to bubble burst. Die head pressure above 30 MPa produces sharkskin melt fracture on the primary tube surface; adding 0.05 wt% to 0.10 wt% of fluoroelastomer processing aid shifts the onset of sharkskin to higher shear rates. The oriented film is tested for free shrink per ASTM D2732 at 120 °C and 135 °C, tensile properties per ISO 527-3, and puncture resistance per ASTM D5748. Final product is a collation shrink film for beverage cans, PET bottles, and glass jars with thickness from 30 µm to 60 µm. For food-contact use, the final article must satisfy EU Regulation 10/2011 overall migration limits per EN 1186; direct contact with fatty food simulants requires article-level verification because low-VA EVA has higher diffusion resistance than high-VA grades but is not universally accepted without extraction testing.

Where the grade functions as a masterbatch carrier for polyolefin packaging applications, twin-screw compounding on a 50 mm co-rotating extruder with 40:1 L/D is operated at screw speed 300 rpm to 500 rpm and barrel temperature 180 °C to 210 °C. The low melt flow rate of 1.5 g/10 min provides sufficient melt strength for strand pelletising; however, die-face cutter water temperature must be kept below 25 °C to prevent agglomerated pellets. A standard carbon black masterbatch formulation contains 50 wt% to 60 wt% EVA 7.5/1.5, 35 wt% to 45 wt% furnace black, and 3 wt% to 5 wt% PE wax. The VA group improves pigment wetting as measured by the filter pressure value method per EN 13900-5. Final masterbatch is let down at 3 wt% to 6 wt% in polyolefin film and moulding compounds. Compliance for food-contact masterbatches depends on end-use restrictions under FDA 21 CFR 177.1350 and EU Regulation 10/2011; the final article must be tested for overall migration per EN 1186 and specific migration of vinyl acetate when relevant. The carrier resin should not be used in formulations containing free amine-based heat stabilisers, because amine by-products can discolour the VA segment and reduce dispersion stability during long residence times.

When EVA 7.5/1.5 Replaces LDPE in Flexible Cap Liner Formulations

Injection moulded liners for flavour-sensitive and moisture-sensitive products use EVA 7.5/1.5 at 30 wt% to 50 wt% in LDPE, with 0.5 wt% to 1.0 wt% precipitated silica as anti-block. The moulding machine is specified with a compression ratio 2.5:1 to 3.0:1, barrel temperatures 180 °C to 200 °C, and clamp force calculated from projected area at 350 bar to 450 bar injection pressure. Mould temperature is held at 20 °C to 40 °C. Melt temperature above 210 °C causes splay and acetic acid odour; below 175 °C high injection pressure produces short shots and gate stringing. The finished liners show lower seal initiation force and improved reseal after repeated opening compared to LDPE alone. Leakage performance is tested per ASTM D4991 with vacuum decay; sensory compliance is assessed under EN 1230 or equivalent panel methods. This application is limited to non-sterile closures because the low-VA grade has not been validated for gamma or ethylene oxide sterilisation at industrial dose ranges. Copper-alloy inserts in the hot runner are avoided because residual VA degradation products attack copper surfaces and can discolour the melt. Warpage on flat liners increases above 1.2 mm when mould temperature exceeds 40 °C; this is controlled by balanced cooling circuits and post-mould shrinkage measurement per ISO 294-4.

For returnable industrial dunnage and electronic component trays, a blend of 40 wt% EVA 7.5/1.5 with 60 wt% LDPE is run on a single-screw extruder feeding a flat die. Melt temperature is 185 °C to 205 °C and polishing roll stack temperature is 70 °C to 90 °C. Sheet thickness is controlled between 1.5 mm and 3.0 mm. The VA-containing phase reduces stress whitening when trays are flexed at low ambient temperatures, while the low melt flow rate maintains sag resistance during thermoforming. Plug-assisted forming is carried out at sheet surface temperatures of 120 °C to 140 °C, measured with an infrared pyrometer; below 110 °C the sheet develops microcracking at the draw corners. The formed trays are not suitable for sustained contact with acetone, ethyl acetate, or aromatic hydrocarbons because the VA segment swells; chemical resistance is screened per ISO 175:2010. Final article load performance is measured by edge crush resistance and drop testing rather than by resin-level tensile data. Published data for this specific EVA grade in thermoformed electronics trays is limited; process setup therefore requires line-side rheometric verification using a capillary rheometer at 190 °C over shear rates 100 s⁻¹ to 1000 s⁻¹. The formulation is incompatible with copper stabiliser packs and should not be processed on extruders with brass screen changers or copper mesh gaskets exposed to the melt stream.